Power electronic component module and method for assembling same

ABSTRACT

This electronic module comprises a metallic base ( 12 ) and electronic power components (D 1 , D 2 , D 3 , D 4 , D 5 , D 6 ) on the base; in which each component, in a group consisting of some of the components, is mounted on the base with a respective electrically insulating and thermally conductive element ( 44 ) being interposed, the other components of the power module being connected electrically to the said base, and in which a peripheral frame ( 14 ) is mounted on the base and incorporates interconnecting elements of electrically conductive materials. 
     The invention is applicable in the field of motor vehicle alternators.

FIELD OF THE INVENTION

The present invention relates to an electronic module comprisingelectronic power components, and a method of assembling such a module.

More particularly, the invention relates to an electronic module of thetype comprising a metallic base and electronic components mounted on thebase, in particular as a rectifier bridge.

STATE OF THE ART

In a known arrangement, the electronic components from which this typeof module is constructed are in the form of individually encapsulatedsilicon chips.

This type of technique considerably increases the size of the module andrenders the components hard to interchange, because each componentsupplier supplies components of specific configuration.

In another known arrangement, which partially overcomes these drawbacks,all of the electronic power components in the module are mounted on thebase. For electrical reasons, some of the electronic power components ofthe electronic module must be electrically insulated from the base. Forthis purpose a layer of electrically insulating material is interposedbetween the base and the said components that are to be insulated. In aknown way, this insulating layer is common to all of the electroniccomponents that have to be insulated. In some modules, all of theelements, including those that must be earthed, may be insulated.

In that case the components are generally in the form of unclad siliconchips, which are easy to interchange.

This method does however have a major inconvenience because it has arelatively high selling cost. In this connection, the electricalinsulator is expensive. Because this insulator is common to all of thepower components which have to be insulated from the base, theinsulating portions situated between the electronic components aresomewhat ineffective for evacuating heat given off by the components inoperation.

In the document DE-A-2 755 404 in accordance with the preamble of claim1, there is described an electronic module, comprising a metallic baseand electronic power components mounted on the base. In a groupconsisting of some of the components, each component is mounted on thebase with a respective element being interposed which is electricallyinsulating and thermally conductive, the other components beingconnected electrically to the said base.

In this way, the selling cost of the module is considerably reducedbecause the electronic components are individually insulated from thebase, while evacuation of heat given off in operation of the componentsis improved.

Nevertheless, a problem is presented because the components areforce-fitted into the base, in such a way that the arrangement of thecomponents in the module cannot be optimised, and the interconnectionbetween the components of the module is not simple to achieve.

SUMMARY OF THE INVENTION

An object of the present invention is to overcome these drawbacks in asimple and inexpensive way.

According to the invention, an electronic module of the type describedabove is characterised in that it includes a peripheral frame mounted onthe base, and in that the frame incorporates interconnecting elements ofelectrically conductive materials.

Thanks to the invention, the interconnection between components issimple to achieve and the arrangement of the components in the module isoptimised. In addition, the frame is simple to make and enables both thebase and the insulating, thermally conductive element to be simplified.Moreover, stresses on the components are reduced because the latter arenot force-fitted.

Interconnection with elements outside the module is also simple to make.

Thus, in one embodiment, the peripheral frame also incorporatesinterconnecting elements of electrically conductive materials in orderto make an interconnection between the components of the module andelements outside the latter.

In an inexpensive embodiment, the peripheral frame is made by mouldingin a plastics material, while the metallic connecting arms are mouldedinto the peripheral frame.

The moulding-in operation preferably provides apertures in theperipheral frame, such as to define zones of electrical contact on thesaid metallic arms.

The module can with advantage further include one or more of thefollowing features, taken separately or in accordance with anytechnically possible combination:

-   -   At least the face of the insulating element that receives a        respective component is coated with a metallic layer.    -   The metallic layer placed on the face of the insulating element        which receives the component is connected to an electrical        connecting terminal located in line with the base.    -   An intermediate support, of a material which is conductive to        both heat and electricity, is interposed between each component        of the said group of some components and a respective insulating        element.    -   At least the face of the element that receives a component is        connected to an electrical connecting terminal.    -   The other electronic components are mounted on the base with an        intermediate support of electrically conductive material        interposed.    -   The power components are provided with a connecting pad mounted        on their top face, to which the conductors are connected so as        to connect the components to the remainder of the circuit of the        module.    -   The insulating element consists of an alumina wafer.    -   Each face of the alumina wafer is coated with a metallic        coating.    -   The metallic layer located on each face of the alumina wafer is        of copper.    -   The module further includes a peripheral frame and a protective        cover, both mounted on the base, and the electronic components        are encapsulated within a flexible protective resin.    -   The module further includes a peripheral frame mounted on the        base and the components are encapsulated in a flexible resin        which is coated with a layer of rigid protective resin.    -   The electronic power components consist of unclad silicon chips.

The invention also provides a method of assembly of an electronic modulecomprising electronic power components, which are in particularconnected as a rectifier bridge for a motor vehicle alternator, on ametallic base, characterised in that it comprises the steps that consistof:

-   -   fixing each component between an intermediate support and        electrical connecting pads;    -   fixing a first group of the components on the base;    -   fixing each component of a second group of the components on a        respective element which is an electrical insulator and a        conductor of heat, which is coated with at least one layer of        electrically conductive material and which is applied on the        base.

Preferably, subsequently to the fixing of the components on the base,there is fixed on the latter a peripheral frame of plastics materialwhich incorporates electrical connecting means, and the connecting padsand the intermediate supports or the electrically conductive layer ofthe said element are connected to the electrical connecting means of theframe.

In a modified version, the said electrically insulating element iscoated with a layer of metallic material which is fixed by brazing onthe base.

In another modified version, the said electrically insulating material,coated with a layer of electrically conductive material, is adhesivelybonded on the base.

In a further embodiment, the said electrically insulating element,coated with a layer of electrically conductive material, is fixed on thebase by application of assembly pressure.

In yet another version, the said electrically insulating element coatedwith a layer of material which is electrically conductive is formed onthe base by spraying an electrically insulating and thermally conductivematerial on the base and by depositing on the latter a layer ofelectrically conductive material.

The invention may be applied with advantage to a motor vehiclealternator comprising a rectifier bridge, a three-phase or six-phasestator, phases output from the stator being rectified by the rectifierbridge, essentially characterised in that the rectifier bridge consistsof an electronic power module including the above mentioned technicalfeatures.

BRIEF DESCRIPTION OF THE DRAWINGS

Further objects, features and advantages will appear from the followingdescription, which is given by way of non-limiting example only and withreference to the attached drawings, in which:

FIG. 1 is a diagrammatic top plan view of part of a module of electronicpower components according to the invention;

FIG. 2 shows the electronic structure of the circuit embodied by theportion of a module shown in FIG. 1;

FIG. 3 shows diagrammatically the mounting of the negative diodes of thecircuit in FIG. 2 on the base of the module according to the invention;

FIG. 4 shows a modified version of the mounting of the negative diodesin the circuit of FIG. 2 on the metallic base of the module according tothe invention;

FIG. 5 shows diagrammatically the mounting of the positive diodes of thecircuit in FIG. 2 on the base of the module according to the invention;

FIG. 6 is a view of the module of FIG. 1, in cross section taken on theline VI—VI and on a larger scale;

FIG. 7 is a view in cross section of a module of electronic powercomponents according to the invention, provided with a protective cover;

FIG. 8 is a view in cross section of a further embodiment of the modulein FIG. 7; and

FIG. 9 shows a further version of an electronic circuit embodied in amodule in accordance with the invention.

FIG. 1 shows a portion of a module of electronic power componentsaccording to the invention, designated by the general reference numeral10.

DESCRIPTION OF EXAMPLES OF EMBODIMENTS OF THE INVENTION

The module 10 consists essentially of a base 12 made of an electricallyconductive material appropriate to the intended application, being forexample in copper, aluminium or steel, and on the outer periphery ofwhich there is fixed a peripheral frame 14, and on which there aremounted electronic power components D1, D2, D3, D4, D5 and D6 in theform of silicon chips. The frame 14 is preferably of electricallyinsulating material, and is for example made by moulding an electricallyinsulating plastics material. It incorporates elements of electricallyconductive material (for example copper or brass) for interconnectionsuch as to make an interconnection between the components of the moduleand elements outside the latter. The frame is for example adhesivelybonded on the base. The incorporation of the electrically conductiveelements preferably consists in moulding metallic connecting arms intothe frame. It will be appreciated that the base 12 is preferably flat,and that the electronic power components can easily be disposed on thelatter.

The frame 14 extends into the interior of the base 12, to define, forexample, three salient portions 100, 101 and 102 which contain themoulded-in arms 103 of connecting terminals 22, 24 and 26 respectively.The moulded-in arm 103 has a terminal zone 104 which is accessible fromoutside in order to make the electrical connection with conductors 16,18 and 20.

As can be seen in FIG. 2, the electronic circuit formed by thesecomponents consists of a double alternating three-phase rectifierbridge.

Thus, the circuit is provided with three positive diodes, namely thediodes designated by the references D1, D3 and D5, together with threenegative diodes, namely the diodes designated by the references D2, D4and D6.

With this construction, the anode of the positive diodes D1, D3 and D5,together with the cathodes of the negative diodes D2, D4 and D6, areconnected by means of the conductors 16, 18 and 20 to means forelectrically connecting the module to a source of supply of alternatingelectrical energy, these means consisting of the three connectingterminals 22, 24 and 26 respectively which are supplied respectivelyfrom phases φ1, φ2 and φ3 of the supply source.

The said connecting terminals 22, 24 and 26 are incorporated by in situmoulding in the frame 14 during the moulding of the latter.

In the embodiment under consideration, in which the module is adapted toconstitute a rectifier module for a motor vehicle alternator, theconnecting terminals 22, 24 and 26 are connected to the outputs of thephases of the stator of the alternator. It is for this reason that theterminals have lugs for fastening the outputs of the phases by crimping.

The stator of the electrical machine, constituting in particular analternator or an alternator starter, may be wound either with wires orwith conductive bars which are preferably of a hairpin configuration,and which are located in slots in the stator. The windings thus producedmay be of the three-phase or six-phase type. The conductors of the saidhairpins are preferably aligned in the slots. For more details,reference should be made to French patent application No. 01 04770.Preferably, the electronic module is carried by the rear bearing which,in the known way, is part of the alternator.

As to the cathode of each of the positive diodes D1, D3 and D5, this isconnected by means of conductors 28, 30 and 32 to terminals or pads 34,36 and 38 for output of rectified current, which form part of aconductive track 39 which is incorporated, in accordance with theinvention, in the frame 14, and which are locally exposed for theelectrical connection of the said connectors. In the conventional way,the conductive track 39 is provided with a B⁺ terminal (not shown) onwhich the positive terminal of the battery of the vehicle is connected.The B⁺ terminal is connected to the conductive track 39 in a mannerknown per se, as for example in French patent application FR 00 08836filed on Jun. 29, 2000. The track 39 consists in this example of ametallic strip moulded into the frame. The arms 39, 103 areinterconnecting strips such that the strip makes the interconnectionbetween the components.

Referring now to FIG. 3, in which only one of the negative diodes D2 hasbeen shown, in a first assembly mode, the negative diodes D2, D4 and D6are directly fixed by brazing, or by means of an appropriateelectrically conductive adhesive, on the base 12 in such a way thattheir anodes are electrically connected to the latter.

A connecting pad 40 of electrically conductive material, for examplecopper, is brazed with the aid of an electrically conductive adhesive onthe top face of each negative diode, that is to say on their cathodes.

The same material is preferably used for mounting the connecting pads 40on these diodes as for the mounting of the latter on the base 12.

Preferably, the pads 40 are made of a material which is a good conductorof heat and has a high calorific capacity, for example copper, and suchas to permit storage and evacuation of heat produced by the diodes inthe course of operation of the latter, in the event of a sharp increasein the voltage at their terminals.

In another version, as can be seen in FIG. 4, in the event that thematerials of which the negative diodes and base 12 are made havedifferent coefficients of expansion, there is interposed between thelatter an intermediate support element 42, which is for example ofcopper, so as to reduce the mechanical stresses imposed on the chips ofthe negative diodes, in particular in the case where the base 12 is madeof aluminium.

As regards the positive diodes D1, D3 and D5, with reference to FIG. 5on which only the diode D1 is shown, each of these diodes is fixed onthe base 12 with a respective element 44 interposed, the latter being anelectrical insulator and a conductor of heat and being in the form of awafer.

As will be understood, the components may be mounted on a single waferor be mounted on respective separate wafers.

For example, this layer 44 is made of alumina. It is covered on at leastone of its mutually opposed major faces with an electrically conductivemetallic layer 46, which is for example of copper.

The alumina layer 44 may be brazed or adhesively bonded on the base.Where it is fixed by brazing, the conductive metallic layer 46 isnecessary because alumina cannot be directly brazed.

However, any other appropriate technique may be used for depositing sucha layer on the base. Thus it is possible to fix it for example byadhesive bonding using an electrically conductive or insulatingadhesive, by application of an assembly pressure on the said wafer, orby spraying alumina, for example in the form of a plasma, on the baseand then covering it with a copper layer.

An intermediate support element 48, made of a material which is a goodconductor of heat and electricity, for example copper, and designed toimprove the diffusion of heat when the vehicle is stationary and toensure the thermal capacity function when the diode is subjected totransitory voltage peaks, is secured by adhesive bonding or brazing onthe wafer 44, the latter being coated with layers 46 of electricallyconductive material.

A chip D1 is then secured by brazing or adhesive bonding, with the aidof an electrically conductive adhesive, on the intermediate support 48in such a way that it rests on the latter through its cathode.

It will be noted that, in the case where the positive chips D1 arebrazed on the intermediate support 48, a method of brazing is preferablyused in which the melting temperature is higher than that used formounting the support 48 on the electrically insulating wafer.

Finally, as in the embodiment described with reference to FIGS. 3 and 4,the upper face of each chip D1 is provided with an electrical connectingpad 50 to which the conductors 16, 18 and 20, for supplying power to therectifier bridge (FIGS. 1 and 6) are connected.

After the components have been mounted on the base, the latter isfurnished with a peripheral frame of plastics material which is providedwith electrical connecting means.

These connecting means are then connected to the connecting pads 40 and50 and to the intermediate supports 48 and metallic layer 46.

At the level of the terminal connecting zone 184, the salient portions100, 101 and 102 preferably have an elevation 105 which enables thelength of the conductors 16, 18 and 20 to be reduced by positioning theterminal connecting zone 107 at the same height as the intermediatesupports 48 or metallic layers 46. Thus, by reducing the length of theconductors 16, 18 and 20, the vibration resistance of the electronicpower module is increased. Preferably, the terminal connecting zone 107is equidistant from the connecting pads 40, 50 of the power components.

With reference now to FIG. 7, the module thus produced is thenencapsulated within a polymerisable flexible resin 52, for example asilicone gel, which is flowed over the module in such a way as to coverall of the electronic components carried by it, and also the wiring withwhich it is provided, the assembly being then covered by a protectivecover 54 mounted on the base.

As can be seen in this Figure, the resin 52 preferably does not fill allof the space bounded by the module and the cover 54, so that it definesa space 56 which enables the resin 52 to expand during operation of themodule.

In another version shown in FIG. 8, the encapsulation of the module iscarried out using a first flexible resin 58, which is for exampleidentical to the resin used in the embodiment described with referenceto FIG. 7, in which the components as well as the conductors areencapsulated.

A rigid second resin 60, for example an epoxy resin, is deposited on theflexible resin layer 58 so as to give mechanical protection to theassembly in place of the cover.

As will be understood, the invention just described, which makes use ofan electrically insulating material which is a good conductor of heatfor mounting a group consisting of some of the electronic components,enables the manufacturing cost of the electronic module to be reducedbecause the amount of insulating material used is able to be reduced.

In addition, the assembly according to the invention enables heat givenoff by the components in operation to be effectively evacuated.

Finally it will be noted that the electronic module according to theinvention is not limited to the embodiments described.

In this connection, although in the examples described above withreference to FIGS. 1 to 6, the conductors by which the anodes of thepositive diodes and the cathodes of the negative diodes are connected tothe phases of the supply source are connected to the top pads of thepositive diodes, the conductors by which the cathodes of the said diodesare connected to the current output terminals are connected to theconductive top faces of the wafers.

It is also possible, in another version and as can be seen in FIG. 9, toconnect the positive diodes to the phases of the current source by meansof conductors 16, 18 and 20 which are connected to the latter, on theone hand, and to the conductive top face of the wafer 48 or the metallayer 46, the rectified current outlet conductors 28, 30 and 32 being,for their part, connected to the output terminals 34, 36, 38 and to thetop pad 40, 50 of these diodes.

Preferably, the electrically insulating and thermally conductivematerials 44 will be sandwiched between two metallic layers 46, whichare for example of copper or aluminium, in such a way as to constitute asub-assembly having a coefficient of expansion which is well adapted toreduce stresses in the brazed joint.

In the drawings, the base and the frame define a housing within whichthe components are mounted and into which the resin 52, 58 is poured.

In FIG. 7, the cover 54 is mounted on the frame. In FIG. 8, the resin isalso mounted on the frame. The frame, which is preferably of anelectrically insulating material, is a protective element for thecomponents.

1. An electronic module, comprising a metallic base (12) and electronicpower components (D1, D2, D3, D4, DS, D6) mounted on the base, in which,in a group consisting of some of the components, each component ismounted on the base with a respective element (44) being interposedwhich is electrically insulating and thermally conductive, the othercomponents being connected electrically to said base, further includinga peripheral frame (14) mounted on the base, wherein the peripheralframe (14) incorporates interconnecting elements of electricallyconductive materials, and wherein at least the face of the insulatingelement (44) that receives a respective component is coated with ametallic layer (46).
 2. A module according to claim 1, characterised inthat the metallic layer (46) placed on the face of the insulatingelement (44) which receives the component is connected to an electricalconnecting terminal (34, 36, 38) located in line with the base.
 3. Anelectronic module, comprising a metallic base (12) and electronic powercomponents (D1, D2, D3, D4, D5, D6) mounted on the base, in which, in agroup consisting of some of the components, each component is mounted onthe base with a respective element (44) being interposed which iselectrically insulating and thermally conductive, the other componentsbeing connected electrically to said base, further including aperipheral frame (14) mounted on the base, wherein the peripheral frame(14) incorporates interconnecting elements of electrically conductivematerials, and wherein an intermediate support (48), of a material whichis conductive to both heat and electricity, is interposed between eachcomponent of said group of some components and a respective insulatingelement (44).
 4. A module according to claim 3, characterised in that atleast the face of the element (48) that receives a component isconnected to an electrical connecting terminal (34,36,38).
 5. Anelectronic module, comprising a metallic base (12) and electronic powercomponents (D1, D2, D3, D4, D5, D6) mounted on the base, in which, in agroup consisting of some of the components, each component is mounted onthe base with a respective element (44) being interposed which iselectrically insulating and thermally conductive, the other componentsbeing connected electrically to said base, further including aperipheral frame (14) mounted on the base, wherein the peripheral frame(14) incorporates interconnecting elements of electrically conductivematerials, and wherein the other electronic components are mounted onthe base with an intermediate support (42) of electrically conductivematerial interposed.
 6. An electronic module, comprising a metallic base(12) and electronic power components (D1, D2, D3, D4, D5, D6) mounted onthe base, in which, in a group consisting of some of the components,each component is mounted on the base with a respective element (44)being interposed which is electrically insulating and thermallyconductive, the other components being connected electrically to saidbase, further including a peripheral frame (14) mounted on the base,wherein the peripheral frame (14) incorporates interconnecting elementsof electrically conductive materials, and wherein that the powercomponents are provided with a connecting pad (40, 50) mounted on theirtop face, to which the conductors (16, 18, 20) are connected so as toconnect the components to the remainder of the circuit of the module. 7.An electronic module, comprising a metallic base (12) and electronicpower components (D1, D2, D3, D4, D5, D6) mounted on the base, in which,in a group consisting of some of the components, each component ismounted on the base with a respective element (44) being interposedwhich is electrically insulating and thermally conductive, the othercomponents being connected electrically to said base, further includinga peripheral frame (14) mounted on the base, wherein the peripheralframe (14) incorporates interconnecting elements of electricallyconductive materials, and wherein the insulating element (44) consistsof an alumina wafer, and wherein each face of the alumina wafer iscoated with a metallic coating (46).
 8. An electronic module, comprisinga metallic base (12) and electronic power components (D1, D2, D3, D4,D5, D6) mounted on the base, in which, in a group consisting of some ofthe components, each component is mounted on the base with a respectiveelement (44) being interposed which is electrically insulating andthermally conductive, the other components being connected electricallyto said base, further including a peripheral frame (14) mounted on thebase, wherein the peripheral frame (14) incorporates interconnectingelements of electrically conductive materials, and further comprising aprotective cover (54) mounted on the peripheral frame (14), wherein theelectronic components are encapsulated within a flexible protectiveresin (52).
 9. An electronic module, comprising a metallic base (12) andelectronic power components (D1, D2, D3, D4, D5, D6) mounted on thebase, in which, in a group consisting of some of the components, eachcomponent is mounted on the base with a respective element (44) beinginterposed which is electrically insulating and thermally conductive,the other components being connected electrically to said base, furtherincluding a peripheral frame (14) mounted on the base, wherein theperipheral frame (14) incorporates interconnecting elements ofelectrically conductive materials, and wherein the components areencapsulated in a flexible resin (58) which is coated with a layer ofrigid protective resin (60).
 10. An electronic module, comprising ametallic base (12) and electronic power components (D1, D2, D3, D4, D5,D6) mounted on the base, in which, in a group consisting of some of thecomponents, each component is mounted on the base with a respectiveelement (44) being interposed which is electrically insulating andthermally conductive, the other components being connected electricallyto said base, further including a peripheral frame (14) mounted on thebase, wherein the peripheral frame (14) incorporates interconnectingelements of electrically conductive materials, and wherein theelectronic power components include unclad silicon chips.
 11. Anelectronic module, comprising a metallic base (12) and electronic powercomponents (D1, D2, D3, D4, D5, D6) mounted on the base, in which, in agroup consisting of some of the components, each component is mounted onthe base with a respective element (44) being interposed which iselectrically insulating and thermally conductive, the other componentsbeing connected electrically to said base, further including aperipheral frame (14) mounted on the base, wherein the peripheral frame(14) incorporates interconnecting elements of electrically conductivematerials, and wherein the peripheral frame (14) is of an electricallyinsulating plastics material, and wherein metallic connecting arms (103,39) are moulded into the peripheral frame (14).
 12. A module accordingto claim 11, characterised in that the moulding-in operation providesapertures (34, 36, 38) in the peripheral frame (14), such as to definezones of electrical contact on the said metallic arms.
 13. A method ofassembly of an electronic module comprising electronic power components(D1, D2, D3, D4, D5, D6), which are in particular connected as arectifier bridge for a motor vehicle alternator, on a metallic base(12), characterised in that it comprises the steps that consist of:fixing each component between an intermediate support and electricalconnecting pads; fixing a first group of the components on the base;fixing each component of a second group of the components on arespective element (44) which is an electrical insulator and a conductorof heat, which is coated with at least one layer (46) of electricallyconductive material and which is applied on the base.
 14. A methodaccording to claim 13, characterised in that, subsequently to the fixingof the components on the base, there is fixed on the latter a peripheralframe of plastics material which incorporates electrical connectingmeans, and the connecting pads and the intermediate supports or theelectrically conductive layer of the said element (44) are connected tothe electrical connecting means of the frame.
 15. A method according toclaim 13, characterised in that the said electrically insulating elementis coated with a layer of metallic material which is fixed on the base.16. A method according to claim 13, characterised in that the saidelectrically insulating element coated with a layer of material which iselectrically conductive is formed on the base by spraying anelectrically insulating and thermally conductive material on the baseand by depositing on the latter a layer of electrically conductivematerial.
 17. A motor vehicle alternator comprising a rectifier bridge,a three-phase or six-phase stator, phases output from the stator beingrectified by the rectifier bridge, characterised in that the rectifierbridge consists of an electronic module according to claim 1.